This invention relates to measuring the location, fluid type, and flow rate of fluids entering a wellbore.
In current practice, measurements are made in the central portion of the wellbore cross-section, such as of spinner rotation rate, fluid density and dielectric constant. These data are then interpreted in an attempt to determine the flow rate at any point along the borehole. Influx (or exit) rate over any interval is then determined by subtracting the flowrates at the two ends of the interval. However, in deviated and horizontal wells with multiphase flow, and also in some vertical wells such methods frequently give erroneous results due to the complex flow patterns within the wellbore giving non-representative readings. All prior production logging measurements are made in these complex flow regimes in the central area of the borehole and yield non-representative results, or have other severe limitations.
The problem of measuring multi-phase flow in conventional production logging is well documented in the literature. Hill, A. D., Oolman, T., 1982, "Production Logging Tool Behavior in Two-Phase Inclined Flow", JPT, October, p. 2432-40 first described the problems using conventional tools in multiphase wells which are deviated more than two degrees from the vertical. They also describe the four main types of tools which are in use. These are referred to as spinner tools, percent-water tools, density tools and flow concentrating flowmeters. Branagan, P., Knight, B. L., Aslakson, J., Middlebrook, M. L., 1994, "Tests Show Production Logging Problems in Horizontal Gas Wells", Oil & Gas Journal, Jan. 10, p. 41-45; Kalman, J. S., 1993, "Biphasic Fluid Studies for Production Logging in Large-Diameter Deviated Wells", The Log Analyst, Nov-Dec., p. 6-10; DING, Z. X. Ullah, K. Huang, Y., 1994, "A Companion of Predictive Oil/Water Holdup Models for Production Log Interpretation in Vertical and Deviated Wellbores", SPWLA 35th Annual Logging Symposium Transactions, June paper; and Nice, S. B., 1993, "Production Logging in Horizontal Wellbores", 5th World Oil et al., Horizontal Well Technol. Int. Conf. (Houston) Proc., sect. 11, November, particularly discuss the problems of measuring multiple phase flow in horizontal or deviated wells. Zhu, D. Hill, A. D., 1988, "The Effect of Flow From Perforation on Two-Phase Flow: Implications for Production Logging"; Proceedings SPE Annual Technical Conference and Exhibition, SPE 18207, October, p. 267-275 show that under some conditions conventional production logs give misleading results even in vertical wells.
It is an object of the present invention to provide apparatus for, and a method of, measuring the flow at the borehole wall as it enters the wellbore and before it becomes mixed with another phase in a complex flow pattern. The invention can also be used to measure outflow (injection) rates and depths.